Tire spin probs
 

Hi Guys (and gals?).
Although I live in the North East its the NE of England, I race a '74 Challenger with a N/A 528 wedge, I'm usually entered in Pro Et class(9.00 - 11.99) . Its also street legal and I occasionally terrorise the streets of my home town during the (short) summer months. I'm new to the board and after some advice from chassis guys and suspension experts. Ok, the problem with my car is wheelspin from launch. Watching a replay on video It goes like this:
1, car rises at front
2, rear slicks wrinkle
3, front wheels now off ground (car has moved forward about 6 inches)
4, rear suspension now seperates from body about 3 inches, slick hammered into the floor (11.5 psi cold)
5, front tyres now about 6 inches off the floor
6, car starts to take weight off the rear tyres (the whole car appears to jump upwards)
7, the rear tyres spin 1/2 turn and the front comes back down.
8, rear tyres grip and the same happens again though to a much lesser degree. (This can happen about three times)

Car has 48.6 % of weight on rear with 1/2 tank of fuel (3916lb W/D). I use a 29.5 x 10.5 slick (11.5 psi cold) on a 8.5 inch rim. Dana 60 rear with drums. Single leaf landrums, Rancho 5 ways and Caltracs. No pinion snubber. Full cage. 2 x 2 Chassis ties and lots of extra bracing for strength. Car is usually real consistent and last time out was 60fting within a 4 100ths in 9 runs. It looks like the rear has too much rise and is topping out the shocks but the shock absorber bushes show no signs of elongation. Car is very sensitive to tyre sidewall stiffness (vague at speed) and the sidewalls usually go before the tread . Watching the vids I'm not suprised after the pounding they take. Ok I value your opinions on this. I'd like to get these Caltracs working like I've seen they can, before I give up and go to ladder bars. Best 60 ft ever is 1.506 and its been close to this a few times. Best ET is 10.13 again I've been close to this a few times. Best Mph is 135.7 (ditto)
Thanks in advance.
Tig UK
Ps the rear shocks are set usually to 5 or 4 seems to make little difference to 60ft times and the fronts are Comp engineering three ways set @ 60 /40. Front end travel is limited by 1.5 inch from max

First off, Welcome to the site. UK huh 8) I also have Cal Tracs and believe if they were ajusted right the car would squat, not rise in the rear. I have recently made some modifications to my engine and as a result have lost traction myself. I plan on reajusting my Cal Tracs this weekend.
Now as it was explained to me today by very knowledgable person,(Scotty)
1. Start with Cal Trac force transfer link in the top hole of the front pivot.
2. Adjust untill its 1/8" from top of the spring. If traction is no good,
3. Adjust to 0 gap.(adjust untill it just touches the top of the spring).
If traction is still no good,
4. Adjust 1/4 turn at a time, testing at each point.

Its also not unusual for proper launch that the left side to be tuned more or less than right side. It is also recommended you do not adjust pass one full turn. This could result in chasis twist.

If car hooks and pulls left, adjust the right side. If it pulls right adjust the
left side.

I will be trying the same thing this Saturday, or Sunday in a factory parking lot in my town.
I will post results. Hope you will do the same.
Good Luck !

Welcome to the site. I am no help. Never used Caltracs. My car is currently a ladder bar car. I made an appointment today with a chassis shop for Oct. 18th to switch to a 4 link set up.

I'm no help either, I've got leaf springs in my car. ;-)

But welcome to the site!

Let's see some pictures of your car!

Thanks for the welcome.
Sorry I forgot to post the settings for preload on the bars. We usually have around 1/2 turn more in the LHS bar. Normally its 1 1/2 turns LHS and 1 turn RHS. We did this to stop the car moving left from launch. I'm unable to use the top hole on the Caltracs as the bolt for the rose joint would interfere with the spring hanger. A friend with a Camaro said that this setting gave more rise in her setup anyway. So I haven't really persued this.
I've tried various preload, front and rear shock settings and the combination we have at the moment is the best so far, but like all hot rodders I'm trying for more. I still can't get rid of the cars tendancy to porpoise.
Next on the list will be to fab a new spring hanger with the front spring mount 1 inch lower, hopefully this will lower the IC and put it under the cars theoretical neutral line giving more squat. Unfortunately we won't be able to try this out 'till next year as the racing season is all but over here in the UK. Still this gives us time to fab 2 1/4 headers, freshen the 'box and replace the valve springs in readiness for next season. I'd love to post a pic but cant see the "attachment" option, is this because HTML is OFF?
Cheers, Tig UK

Tig, at first mine wouldn't go into the top hole either. we wound up grinding the head of the bolt down untill it did work. As for the picture you'll have to wait for Mikel to respond. He is the expert on that.

When the new spring hanger is made, we'll make it so that either position will be accessible. Oh they're moved inboard so that makes it tougher still.
Cheers. Tig Uk

Tig, check out this post on rear suspension. Maybe this can help you.

http://www.mopartech.net/phpBB2/viewtopic.php?t=29

Thanks for that. Interesting reading, I had my springs re-arched to give better clearance for taller slicks. I guess this is contributing to the rise problem that I have. I've also just been in the garage to check the shackle angle. Its not ideal but is angled to the rear. However a strong launch must pull the shackle forward, Having said that something must stop the spring/shackle from going over TDC and snapping to the front. So maybe its OK. Part of that thread mention IC's and thats where my train of thought is leading me at the moment.
Tig

Oddly enough, the "bad" picture in that link is my car, from when I first installed the Super Stock springs. The angle of the shackle settled down after a few days, it's a lot more straight than it was. However, from what I remember, you can't get the "optimum" angle on the shackle without installing a block between the shackle mount and the frame.

OHOAD, That was a good post you linked to. =D> Thanks.
I am going to go peak under the rear and see where my rear shackles are at. Could be the reason for the bad 60'

Mopower71, what do you have for rear suspension ?

Mikel, you use ss springs, what did you use before this?

Stock springs(that's what they look like) and a pinion snubber.
The springs are moved in using the offset shackle kit.
The rear side of the springs still have the clamps. These should be removed, correct?
The rear shackles are almost vertical, a very slight angle to the rear. If I had to guess, less than a 1/4".
I should make a block to move the hanger forward another 3/4".
Maybe this will help the 60'

30 year old stock springs. They were so worn out, that when I stood on them (after they were out of the car, of course), they flattened out. They're not supposed to do that. I stood on one of the new springs and it barely moved.

Thew new ones are actually Mancini Pro-Stock springs, not the Mopar Super Stock springs. Pretty much the same, though.

My shackles are angled same as yours 1/4" to rear of mount. I have stock leafs also. My bands are on, and I have Cal Tracs. I really don't know what cutting the bands does or will do for you. Let it wrap up easier?
My car was hooking pretty good till I put in the MSD. I'm gonna try tuning it some before I think of moving the hangers more forward on the frame.
If for some reason I can't get it to hook I will try it.

Mikel, did you use any thing else on those stock springs, (snubber, traction bars)? Do you remember the angle of the shackles? Also how was your traction as compaired to now?

No, I didn't use anything on the stock springs. And I don't recall what the angle was beforehand.

Traction is better, now. Especially with the new slicks on there.

From what I remember, cutting the bands was supposed to allow the leafs to spread out when you launch, which I assume would try to plant the rear end harder. When I had the stock springs in my car, I cut the bands off but I didn't see any difference.

Hey Tig - nice car!

https://www.northeastbracketracing.c....php?pic_id=82

I was expecting to see your head on the other side of the vehicle, though. ;-)

Cheers mikel.. Here's another pic.

Tig, Very nice car

Thanks guys. If you're interested in what us Brits get up to, you could check out this web site. All the credits for those pics go to Anni.
http://cgi.feelthenoise.plus.com/

Cheers, Tig

This may help
 

8) You may be " Bouncing" of the tires when you hit them that hard.

I run a low 6 sec s10 with a 580bbc. I was having the same problem and found by using video tape I was hitting the tires so hard the car was bouncing of the tires and unloading. I put 3 more clicks in the rear shocks and problem solved. As you increase launch rpm you may have to increase the shock stifness even more. Also for each three clicks on the rear throw a extra on click on the front.

Footbrake cars need a looser setup than a transbrake car.

This may help.

Dog House was that your S10 that had the nasty crash with the Camaro ? :shock:

I had the same problem with my cuda. I am running a 340 with nos et 10.75@127. Beleive it or not I put an 8 point cage in it and the problem went away. I was bending the car in the middle.